Two-way radio communication systems typically include a plurality of dispatch consoles and communication units, such as mobile or portable radio subscriber units, that are geographically distributed among various base sites and dispatch sites. The communication units wirelessly communicate with the base sites and each other, and are often logically divided into various talkgroups. Each talkgroup organizes a number of subscriber units into a one-to-many communication scheme where, when one person talks (transmits) in the talkgroup, all others in the talkgroup hear the speaker. Talkgroups can be included in one or more multi-groups. A multi-group is an organization of several talkgroups, and when one person talks in the multi-group, every subscriber available in each talkgroup of the multi-group will hear the multi-group speaker. Communication systems can be organized as trunked systems, where a plurality of radio frequency (RF) communication resources are allocated amongst multiple users or groups by assigning the base sites and RF channels within a coverage area on a call-by-call basis, or as conventional (non-trunked) systems where RF communication resources are dedicated to one or more users or groups. In trunked systems, or in mixed trunked and conventional systems, there is usually provided a central controller/server (sometimes called a “zone controller”) for allocating RF communication resources among a group of sites. The zone controller may reside within a single device or multiple devices and may be located at a fixed equipment site or may be distributed among the base sites.
Calls among the communication units are typically of the dispatch type, or better known as push-to-talk (PTT). Each time a communication unit is keyed to begin a call, the call is assigned to an available wireless channel. The originating communication unit begins transmitting on the assigned channel and continues to transmit on the assigned channel until the communication unit has been dekeyed (de-keyed) by the user. Other communication units in an associated talkgroup also switch to the assigned channel and begin listening to the call.
In current communication systems communication units initiating a talkgroup call continue transmitting while the communication unit remains “keyed” (the transmit button pressed to transmit). This often results in a problem if there is a need to stop a communication unit from transmitting before it has dekeyed. For example, if a dispatch operator needs to transmit an urgent call, or if a multi-group call is initiated that has priority over the talkgroup call, there is no way to signal the transmitting communication unit to stop transmitting and listen to the call from the dispatch site or multi-group caller.
Accordingly, there is a need for a system and method for interrupting a transmitting half-duplex communication unit during the transmission of a call.